Food intolerance

Food intolerance is a detrimental reaction, often delayed, to a food, beverage, food additive, or compound in foods producing symptoms.

Food hypersensitivity is used to refer broadly to both food intolerances and food allergies.

Food intolerance refers to reactions to food other than food allergy. 

Estimates of the prevalence of food intolerance vary widely from 2% to over 20% of the population.

However, confirmed prevalences varied from 0.8% to 2.4%. 

For intolerance to food additives the prevalence varied between 0.01 and 0.23%.

Food allergies are immune reactions, typically an IgE reaction caused by the release of histamine but also encompassing non-IgE immune responses.

This mechanism causes allergies to typically give immediate reaction from a few minutes to a few hours to foods.

Food intolerances can result from the absence of specific chemicals or enzymes needed to digest a food substance, result of an abnormality in the body’s ability to absorb nutrients, can occur to naturally occurring chemicals in foods.

Food intolerances can be caused by enzymatic defects in the digestive system, can also result from pharmacological effects of vasoactive amines present in foods (e.g. histamine), among other metabolic, pharmacological and digestive abnormalities.

Allergies and intolerances to a food group may coexist with separate pathologies; for example, cow’s milk allergy (CMA) and lactose intolerance are two distinct pathologies.

Food intolerance are all other adverse reactions to food. 

Subgroups include enzymatic/lactose intolerance due to lactase deficiency, pharmacological-reactions against biogenic amines, histamine intolerance, and undefined food intolerance/against some food additives.

Drugs sourced from plants, such as aspirin, can also cause these kinds of reactions.

Food intolerance reactions can be pharmacologic, metabolic, or gastro-intestinal responses to foods or food compounds. 

Food intolerance does not include either psychological responses or foodborne illness.

It can be difficult to determine the poorly tolerated substance in food, as as reactions can be delayed, dose-dependent, and a particular reaction-causing compound may be found in many foods.

Food intolerance is an abnormal physiological response. 

Metabolic food reactions are due to inborn or acquired errors of metabolism of nutrients, such as in lactase deficiency, phenylketonuria and favism.

Pharmacological reactions are due to low-molecular-weight chemicals which are natural compounds, such as salicylates, amines and glutamates or to food additives, such as preservatives, coloring, emulsifiers and flavor enhancers. 

These chemicals are capable of causing biochemicalside effects in susceptible individuals.

GI reactions can be due to malabsorption or other GI tract abnormalities.

Immunological responses by non-IgE immunoglobulins, where the immune system recognizes a particular food as a foreign body.

Toxins may either be present naturally in food, be released by bacteria, or be due to contamination of food products.

Toxic food reactions are caused by the direct action of a food or substance without immune involvement.

Psychological reactions involve clinical symptoms caused by emotions associated with food. 

Food intolerance is more chronic, less acute, less obvious in its presentation, and often more difficult to diagnose than a food allergy.

It can be difficult to determine the offending food causing a food intolerance because the response generally takes place over a prolonged period of time. 

Food intolerance symptoms usually begin about half an hour after eating or drinking the food in question, but sometimes symptoms may be delayed by up to 48 hours.

Food intolerance symptoms can affect: the skin, respiratory tract, gastrointestinal tract (GIT) either individually or in combination. 

Skin findings include, skin rashes, urticaria (hives), angioedema, dermatitis,and eczema.

Respiratory tract symptoms of food intolerance can include: nasal congestion, sinusitis, pharyngeal irritations, asthma and an unproductive cough. 

GI symptoms include: mouth ulcers, abdominal cramp, nausea, gas, intermittent diarrhea, constipation, irritable bowel syndrome (IBS), and may include anaphylaxis.

Food intolerance is associated with: irritable bowel syndrome, inflammatory bowel disease, chronic constipation, chronic hepatitis C infection, eczema, NSAID intolerance, respiratory complaints,including asthma, rhinitis and headache, functional dyspepsia, eosinophilic esophagitis and ear, nose and throat illnesses.

Reactions to chemical components of the diet may be more common than true food allergies: organic chemicals occurring naturally in  variety of foods, animal and vegetable, more often than to food additives, preservatives, colorings and flavorings, such as sulfites or dyes.

Both natural and artificial ingredients may cause adverse reactions.

The degree of sensitivity varying between individuals.

Symptoms of food intolerance may begin at any age, and may develop quickly or slowly. 

Food intolerance triggers range widely from a viral infection or illness to environmental chemical exposure. 

Chemical intolerance to foods occurs more commonly in women, as many food chemicals mimic hormones.

A deficiency in digestive enzymes can also cause some types of food intolerancesL Lactose intolerance is a result of the body not producing sufficient lactase to digest the lactose in milk; enzyme deficiency of hereditary fructose intolerance.

Celiac disease, an autoimmune disorder caused by an immune response to the protein gluten, results in gluten intolerance and can lead to temporary lactose intolerance.

The most widely distributed naturally occurring food chemical capable of provoking reactions is salicylate.

Tartrazine and benzoic acid that are well recognized in susceptible individuals.

Benzoates and salicylates occur naturally in many foods, including fruits, juices, vegetables, spices, herbs, nuts, tea, wines, and coffee. 

Salicylate sensitivity causes reactions to not only aspirin and NSAIDs but also foods in which salicylates naturally occur, such as cherries.

Natural chemicals which commonly cause reactions and cross reactivity include amines, nitrates, sulphites and some antioxidants. 

Chemicals involved in aroma and flavor are often suspect to cause food intolerance.   

Salicylate-containing foods include apples, citrus fruits, strawberries, tomatoes, and wine, while reactions to chocolate, cheese, bananas, avocado, tomato or wine point to amines as the likely food chemical. 

Excluding single foods does not necessarily identify the chemical responsible as several chemicals can be present in a food, the patient may be sensitive to multiple food chemicals and reaction more likely to occur when foods containing the triggering substance are eaten in a combined quantity that exceeds the patient’s sensitivity thresholds.

People with food sensitivities have different sensitivity thresholds, and so more sensitive people will react to much smaller amounts of the substance.

Diagnosis of food intolerance can include hydrogen breath testing for lactose intolerance and fructose malabsorption, supervised elimination diets, and ELISA testing for IgG-mediated immune responses to specific foods. 

It is important to be able to distinguish between food allergy, food intolerance, and autoimmune disease in the management of these disorders. 

Non-IgE-mediated intolerance is more chronic, less acute, less obvious in its clinical presentation, and often more difficult to diagnose than allergy.       

Skin tests and standard immunological studies are not helpful.

Elimination diets must remove all poorly tolerated foods, or all foods containing offending compounds. 

Immunoglobulin (IgG) tests measure the types of food-specific antibodies present. 

There are four types of IgG, IgG1 makes up 60-70% of the total IgG, followed by IgG2 (20-30%), IgG3 (5-8%), and IgG4 (1-4%). 

IgG4 presence indicates that the person has been repeatedly exposed to food proteins recognized as foreign by the immune system which is a normal physiological response of the immune system after exposure to food components.

Elimination of foods based on IgG-4 testing in IBS patients results in an improvement in symptoms, but the positive effects of food elimination are  more likely due to wheat and milk elimination than IgG-4 test-determined factors.

The IgG-4 test specificity is questionable as healthy individuals with no symptoms of food intolerance also test positive for IgG-4 to several foods.

To obtain a final confirmation a double blind controlled food challenge must be performed.

Sensitization and the acquisition of tolerance can begin in pregnancy.

The main sensitization to foods is  during early infancy when the immune system and intestinal tract are still maturing.

There is no conclusive evidence to support the restriction of dairy intake in the maternal diet during pregnancy.

Soy formulas cannot be recommended for prevention of allergy or food intolerance in infants. 

In the prevention of allergic diseases in high-risk infants, particularly in early infancy the most effective dietary regimen is exclusive breastfeeding for at least 4–6 months or, in absence of breast milk, formulas with documented reduced allergenicity for at least the first 4 months, combined with avoidance of solid food and cow’s milk for the first 4 months.

E limination diets are not everyday diets but intended to isolate problem foods and chemicals.

It takes around five days of total abstinence to unmask a food or chemical/

During the first week on an elimination diet withdrawal symptoms can occur but it takes at least two weeks to remove residual traces. 

If symptoms have not subsided after six weeks, food intolerance is unlikely to be involved and a normal diet should be restarted. 

Withdrawals are often associated with a lowering of the threshold for sensitivity.

After two or more weeks if the symptoms have reduced considerably or gone for at least five days then challenge testing can begin: selected foods containing only one food chemical, to isolate it if reactions occur.

New challenges should only be given after 48 hours if no reactions occur or after five days of no symptoms if reactions occur.

Children with intolerance to milk respond to diet which excludes cow’s milk protein and the majority of patients succeed in forming tolerance.

Children with non-IgE-mediated cows milk intolerance have a good prognosis, but those with IgE-mediated cows milk allergy in early childhood have a significantly increased risk for persistent allergy, development of other food allergies, asthma and rhinoconjunctivitis.

Perceived food intolerance is a common problem with significant nutritional consequences in a population with IBS. 

70% of IBS patients have symptoms related to intake of food, and 62% limited or excluded food items from the diet. 

Some patients with chronic fatigue syndrome report food intolerances that can exacerbate symptoms.

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